1. Field of the Invention
The present invention relates to an information memory apparatus and a library apparatus and, more particularly, to an information memory apparatus and a library apparatus for recording data on a magnetic tape.
Recently, the capacity of magnetic tapes has been increased due to as increase in recording density and an increase in the number of tracks. For example, in a cartridge-type magnetic tape used for a large-scale computer system, the data recording capacity of a single-volume tape cartridge has increased from an original capacity of 200 MB, 18 tracks to 800 MB, 36 tracks, which capacity is four times the original capacity. This was achieved by serpentining the 18 tracks and increasing the tape to a double length. Additionally, since the memory capacity can be increased about three times on average by using a data compression function, the data recording capacity of a single tape cartridge may be increased up to about 2.4 GB.
However, many users use only the leading part of the tape cartridge despite the increase in data recording capacity. That is, the actually used memory capacity of each tape cartridge has not been increased in practical use. A reason for this is that there may be many data sets (private volumes) assigned for an individual user or that the tape cartridge may be used for a task which requires a small amount of data other than large backup data. That is, the tape cartridge may be used by an individual or used for a single task which handles a small amount of data.
In order to use the tape cartridge more efficiently, it is suggested that a plurality of files be provided on a single-volume magnetic tape, which is referred to as a multi-file tape. This allows a single-tape cartridge to be shared with a plurality of persons or a plurality of tasks.
2. Description of the Related Art
FIG. 1 is a block diagram of an example of a conventional magnetic tape memory apparatus. The magnetic tape memory apparatus 51 shown in FIG. 1 comprises a magnetic tape unit 52 and a magnetic tape controller 55. The magnetic tape unit 52 records/reproduces data on a magnetic tape. The magnetic tape controller 55 controls a connection between the magnetic tape unit 52 and a host computer 54.
The magnetic tape controller 55 comprises a channel adapter 56, a device adapter 57, a buffer memory 58 and a control memory 59. The channel adapter 56 connects the magnetic tape controller 55 to a channel of the host computer 54. The device adapter 57 connects the magnetic tape controller 55 to the magnetic tape unit 52. The buffer memory 58 temporarily stores data input to or output from the magnetic tape unit 52. The control memory 59 maintains a relationship of logical volumes between the magnetic tape unit 52 and the host computer 54.
In the conventional magnetic tape memory apparatus 51, a format of the magnetic tape is determined so that a single file is recorded on a single volume of magnetic tape because it is assumed that a large capacity file is created with a single magnetic tape.
FIG. 2 is an illustration of a format of a single file recorded on a conventional magnetic tape.
In the conventional magnetic tape, a single logical volume is set in a single volume tape. The tape format of the conventional tape comprises a logical volume name memory area VOL1, headers HDR1 and HDR2, a file storing area FILE, end of file areas EOF1 and EOF2 and a tape winding area TWA, in that order, beginning from a leading end of the tape. The logical volume name memory area VOL1 is provided for identifying the logical volume set for the tape. The headers HDR1 and HDR2 store information related to a file such as capacity and contents of the file. The file storing area FILE stores the file. The areas EOF1 and EOF2 store information representing the end of file. The tape winding area TWA represents the end of the tape.
In the above-maintained tape format, only a single file is stored in a single volume magnetic tape cartridge. Accordingly, only a leading portion of the magnetic tape may be used when the tape cartridge is used with a system in which most of files created in the system contain a small amount of data or most files are managed by an individual. That causes a condition in which a large portion of tape will never be used. This reduces a used area rate of the magnetic tape for each volume.
In order to increase the used area rate of the magnetic tape, an apparatus is suggested which has a multi-file function for storing a plurality of files on a single-volume magnetic tape.
FIG. 3 is an illustration of a format of a conventional multi-file tape. As shown in FIG. 3, in the conventional multi-file tape, a single-volume tape is considered as a single logical volume. A plurality of files FILEO to FILEN are set in the single logical volume. Access to one of the files can be made by designating a volume order number (VOL)/serial number (SEL) and a data set order number (LABEL) in accordance with the DD text of the job control language (JCL) specified in the operating system (OS) of the host computer. As mentioned above, a plurality of files can be set in a single magnetic tape cartridge. About 10,000 files may be created in a single tape according to the current specification.
In this apparatus, VOL/SER and LABEL must be set in the operating system of the host computer. This is inconvenient for a user, and thus this system is not practically used.
This inconvenience is caused by the fact that a file cannot be set as a logical volume. Japanese Laid-Open Patent Application 6-324813 suggested a system in which a plurality of logical volumes can be set in a single volume magnetic tape. In this magnetic tape apparatus system, the magnetic tape must be rewinded to an initial position when accessing a logical volume which was previously accessed. This requires a long accessing time, and thus is not efficiently used for a job shared by a plurality of users or a plurality of tasks.